The present invention generally relates to the field of magnetic sensors for sensing the position of a structure over a predetermined range of movement, and more specifically relates to a non-contacting magnetic position sensor having shaped poles pieces to provide a magnetic field having a varying magnetic flux density field strength.
Magnetic position sensors are devices that generate a change in electronic signal output that is indicative of the sensed movement of a mechanical component, such as, for example, a control shaft or rotor in the case of rotational position sensors or a carrier mechanism or linkage in the case of linear position sensors. Preferably, the change in electronic signal is achieved without physical contact between the mechanical component and the magnetic sensing element. In non-contacting magnetic position sensors, one or more magnets are used to provide a magnetic field having a magnetic field strength or flux density that varies as a function of linear or rotational position.
Variation in the magnitude of the magnetic field strength or flux density is detected by an appropriate sensing device, such as, for example, a Hall-effect element or magneto-resistive element. The magnitude of the magnetic flux density is translated through the sensing device and converted to a voltage or current output signal that is uniquely representative of a specific position of a mechanical component relative to the magnetic field. Preferably, the magnetic position sensor provides a substantially linear relationship between electronic signal output and the position of the mechanical component. In addition to providing a linear relationship, minimizing hysteresis is also a desirable feature in most magnetic sensor applications. While annealing the magnets can reduce magnetic hysteresis, the annealing process can never eliminate magnetic hysteresis entirely.
To generate a magnetic field having a substantially linear profile, those skilled in the art sometimes resort to complicated magnet shapes. For example, U.S. Pat. No. 5,995,881 to White et al. discloses a magnetic circuit that utilizes tapered magnets to provide a magnet field having a varying magnetic field strength. However, magnetic circuits that rely on geometric shaping of the magnets to provide a varying magnetic field commonly suffer from performance and/or manufacturing limitations. For example, providing a magnetic circuit having a linearly varying magnetic field strength is difficult to achieve via magnet shaping due to non-uniformity in material composition and/or complexities in the geometric configuration of the magnet. Additionally, shaped magnets often include magnetic flux xe2x80x9chot spotsxe2x80x9d that effect localized magnetic field strength. Moreover, non-standard magnetic materials are typically used to manufacture magnets having irregular shapes and configurations. Moldable plastic materials are sometimes used to form certain types of irregular shaped magnets. It is often difficult, however, to control the density of the magnetic material. Additionally, use of magnets formed of a moldable plastic material is usually not possible in extreme temperature environments. Moreover, complicated magnet shapes often lead to increased manufacturing costs and limitations on package size. The use of non-standard magnet compositions also tends to increase manufacturing costs.
Magnetic position sensors may be used in a wide variety of applications. For example, magnetic position sensors are used extensively in the automotive industry to monitor the status and position of various automotive components. Notably, position sensors that are used in automotive-related applications typically experience virtually constant movement and/or mechanical vibration while the automobile is in operation. To that end, such sensors must be constructed of mechanical and electrical components that are assembled in such a manner as to minimize the effects of misalignment and/or mispositioning to allow the sensor to operate in a sufficiently accurate and precise manner over the sensor""s projected lifespan. Moreover, automotive position sensors are typically subjected to relatively harsh thermal environments, and therefore must be designed to withstand extreme temperatures and temperature gradients. Typically, automotive sensors must be able to function properly within a temperature range of at least xe2x88x9240 degrees Celsius to 200 degrees Celsius. Additionally, automotive position sensors must usually satisfy relatively high performance criteria, particularly with regard to sensor accuracy and repeatability.
Thus, there is a general need in the industry to provide an improved magnetic position sensor. The present invention satisfies this need and provides other benefits and advantages in a novel and unobvious manner.
The present invention is directed to a magnetic position sensor having shaped pole pieces to provide a magnetic field having a varying magnetic flux density field strength. While the actual nature of the invention covered herein can only be determined with reference to the claims appended hereto, certain forms of the invention that are characteristic of the preferred embodiments disclosed herein are described briefly as follows. However, it should be understood that other embodiments are also contemplated as falling within the scope of the present invention.
In one form of the present invention, a magnetic sensor is provided which includes a pair of magnets and a pair of shaped pole pieces positioned adjacent respective ones of the magnets and spaced apart to define an air gap having a varying width along a length thereof. The magnets and the shaped pole pieces cooperate to provide a magnetic field having a magnetic flux density that varies along the length of the air gap, with a magnetic flux sensor positioned within the magnetic field to sense varying magnitudes of magnetic flux density along the length of the air gap and to generate an output signal representative of a position of the magnetic flux sensor relative to the magnetic field.
In another form of the present invention, a magnetic sensor is provided which includes a pair of magnets and a pair of shaped pole pieces positioned adjacent respective ones of the magnets and spaced apart to define an air gap, with at least one of the shaped pole pieces including a portion of varying thickness. The magnets and the shaped pole pieces cooperate to provide a magnetic field having a magnetic flux density that varies along a length of the air gap adjacent the portion of varying thickness, with a magnetic flux sensor positioned within the magnetic field to sense varying magnitudes of magnetic flux density along the length of the air gap adjacent the portion of varying thickness and to generate an output signal representative of a position of the magnetic flux sensor relative to the magnetic field.
In yet another form of the present invention, a magnetic sensor is provided which includes at least two magnets and at least two shaped pole pieces positioned adjacent respective ones of the magnets and being spaced apart to define a first air gap and a second air gap, with the magnets and the shaped pole pieces cooperating to provide a first magnetic field having a magnetic flux density that varies along a length of the first air gap, and a second magnetic field having a magnetic flux density that varies along a length of the second air gap. A magnetic flux sensor is provided which includes a first magnetic flux sensor element positioned within the first magnetic field to sense varying magnitudes of magnetic flux density along the length of the first air gap, and a second magnetic flux sensor element positioned within the second magnetic field to sense varying magnitudes of magnetic flux density along the length of the second air gap, and wherein the first and second magnetic flux sensor elements cooperate to generate an output signal representative of a position of the magnetic flux sensor relative to the first and second magnetic fields.
In still another form of the present invention, a magnetic sensor is provided which a pair of magnets and pair of shaped pole pieces positioned adjacent respective ones of the magnets and spaced apart to define an air gap. The magnets and the shaped pole pieces cooperate to provide a magnetic field having a magnetic flux density that varies along a length of the air gap. A first magnetoresistive element is positioned within the magnetic field to sense a varying magnitude of the magnetic flux density along a length of the air gap, and a second magnetoresistive element is positioned within an auxiliary magnetic field having a substantially uniform magnetic flux density. The first and second magnetoresistive elements cooperate to generate an output signal representative of a position of the first magnetoresistive element relative to the magnetic field.
It is one object of the present invention to provide an improved magnetic sensor having shaped poles pieces to provide a magnetic field having a varying magnetic flux density field strength.
Further objects, features, advantages, benefits, and aspects of the present invention will become apparent from the drawings and description contained herein.